Wire wound electrical resistor



Jan. 5, 1965 J. M. RAMRATH 3,164,797

WIRE WOUND ELECTRICAL RESISTOR Filed D80. 5;1963

United States Patent Ofiice 3,164,797 Patented Jan. 5, 1965 3,164,797WIRE WOUND ELECTRICAL RESISTOR Joseph M. Ramrath, Mattapan, Mass,assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis. FiledDec. 5, 1963, Ser. No. 328,328 6 Claims. (Cl. 33862) This inventionrelates generally to wire wound electrical resistors adapted forimmersion in a cooling medium such as oil.

In some electric circuit breakers, for example, the contacts areimmersed in oil and a resistor also immersed in the oil is connectedacross each set of contacts so as to be in parallel with the are drawnwhen the contacts separate. This is done to equalize the recoveryvoltage across two or more arcs in series and to otherwise influence theinterrupting performance of the circuit breaker, particularly duringline or capacitor switching. Such resistors, especially those ofrelatively low ohmic value, comprise large amounts of resistancematerial (volume being directly proportional to the PR losses in theresistance material) and even though current flow therethrough is ofvery short duration, the resistance material must absorb considerableamounts of electrical energy and dissipate it in the form of heat to thesurrounding oil. Because such resistors are large and handle relativelyhigh voltages (as much as 230 kv. in some instances), it is necessary toinsulate them to permit their installations in the limited spaceavailable within the circuit breaker. However, since the temperaturerise in the resistance material must be kept low to preserve its lifeand since the insulation acts as a heat barrier, it requires an unduelength of time for heat dissipation. Thus, if there is frequentlyrepeated breaker operation, the resistor may become dangerouslyoverheated.

One presently known type of relatively low ohmic value resistor unitcomprises a multiplicity of coil segments stacked adjacent one anotheron a spindle and the entire unit is covered with insulation. Each coilsegment comprises a ribbon of flat resistance wire coated withinsulating material and wound upon itself. The coil segments areelectrically connected in series and in such a manner so that theresistor unit is substantially noninductive when current flowstherethrough. A resistor unit of this type is subject to the problemdescribed above and is relatively costly to manufacture.

Accordingly, it is an object of the present invention to provide new andimproved resistor units which are adapted for submersion in an arcextinguishing fluid such as oil.

Another object is to provide resistor units of the aforesaid characterwhich employ a maximum of resistance material and a minimum ofelectrical insulating material and which are adapted to dissipaterapidly large amounts of heat to the surrounding oil.

Another object is to provide resistor units of the aforesaid characterwherein oil flows around the exterior of and through the interiorthereof and wherein all of the resistance material employed is in directcontact with the oil.

Another object is to provide resistors of the aforesaid character whichare simpler in construction than known devices, which are relativelyeconomical to fabricate and are reliable in use.

Another object is to provide a resistor unit of the aforesaid characterwhich employs two oppositely wound coils and is substantiallynoninductive.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates several preferred embodiments ofthe present invention but it is to be understood that the embodimentsillustrated are susceptible to modification with respect to detailsthereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is a side elevational view, partly in section, of a substantiallynoninductive electrical resistance unit incorporating the presentinvention;

FIG. 2 is an end view, partly in section, of the resistor unit shown inFIG. 1;

FIG. 3 is a side elevational view, partly in section, of anotherembodiment of an inductive electrical resistor unit incorporating thepresent invention; and

FIG. 4 is an end view partly in section, of the resistor unit shown inFIG. 3.

Referring to FIGS. 1 and 2, the numeral 14! designates a substantiallynoninductive resistor unit incorporating the present invention which isvertically mounted between suitable supporting members 12 in spacedrelationship thereto. It is to be understood that when in use resistorunit 1% is intended to be entirely immersed in a cooling and insulatingmedium, such as oil, contained within an electrical device such as anoil type circuit breaker.

Resistor unit 10 comprises a pair of spaced apart end plates 14- and 16fabricated of insulating material. Since the end plates 14 and 16 areunderstood to be substantially identical to each other, only the formerwill be hereinafter described in detail. End plate 14 is circular inform and is provided with a plurality of radially disposed slots 18 foraccommodating wire supporting members or strips hereinafter described.In the embodiment shown, eight slots 18 are provided and provedsatisfactory but it is to be understood that some other number of slotscould be employed. End plate 14 is further provided with a plurality ofholes or perforations 20, eight being shown, for permitting oil flowthrough the interior of the resistor unit 16). End plate 14 is alsoprovided with a plurality of tapped holes 22 around its periphery toaccommodate screws 24 which secure an insulating and protective housing26 of cylindrical shape in place. End plate 14 is provided with acentral opening 28 for accommodating means, such as a spindle 38, whichadapts it for mounting to the supporting member 12 in spacedrelationship thereto.

The pair of end plates 14 and 16 are axially aligned so that the slots18 therein are in registry and each pair of such registering slotsaccommodates an inner mounting strip 32 and an outer mounting strip 34,each of which is made of insulating material. Each inner mounting strip32 is in the form of an elongated member having a plurality of wireengaging notches 36 along the edge thereof which faces outwardly when itis disposed in its slots 18 in the end plates 14 and 16. Each innermounting strip 32 is also understood to be provided with a pair ofindentations 38 on its inwardly facing edge for engagement with thebottom of the slots 18 in the end plates 14 and 16, respectively, whichserve for alignment purposes and to give added rigidity to resistor unit10.

Means are provided to secure each inner mounting strip 32 to the endplates 14 and 16. Thus, each inner 1nount-' ing strip 32 projects ashort distance beyond the end plates 14 and 16 and is provided with asmall hole 4%) for accommodating a wire 42 which is threaded througheach small hole in all the inner mounting strips and twisted orotherwise fastened together at its ends to hold the inner mountingstrips in place.

Electrical terminals 44 and 46 are mounted at opposite ends of one ofthe inner mounting strips 32 adjacent the outer faces of the end plates14 and 16, respectively. The terminals 44 and 46 are located so as notto interfere with the placement or removal of housing 26. Duringassembly and after the inner mounting strips 32 are in place, a firstlength 48 of coiled resistance wire is con- :3 nected at one of its endsto terminal 4-4, is wound on the inner mounting strips 32 to form afirst or inner coil 50, and is connected at its other end to terminal46. More particularly, for example, the first length 48 of resistancewire is wound in a left-hand direction and laid in the first row ofnotches as in the inner mounting strips 32 nearest end plate 14. Afterthe first row of notches is occupied, the wire is laid in the second rowand so on until all rows of notches have been utilized.

Each outer mounting strip 34 is in the form of an elongated memberhaving a plurality of wire engaging notches 52 along the edge thereofwhich faces outwardly when it is disposed in its slots 13 in the endplates 14 and 16. In the embodiment shown, outer mounting strip 34 isprovided with the same number of notches as there are notches 36 in theunderlying inner mounting strip 32.

Means are provided to secure each outer mounting strip 34 in place.Thus, each inner mounting strip 32 is provided with a tapped hole 54near its opposite ends and each outer mounting strip 34 is provided withan untapped hole 56 near its opposite ends which register with thecorresponding tapped hole 54 in the inner mounting strip. A screw orbolt 58 extends through an untapped hole 56 in outer mounting strip 34and is threaded into a tapped hole 54 in inner mounting strip 32 tosecure the former to the latter.

During assembly and after the outer mounting strips 34 are in place, asecond length as of coiled resistance wire is connected at one of itsends to terminal 44, is wound on the outer mounting strips 34 to form asecond or outer coil 62, and is connected at its other end to terminal46. In order for resistor unit it to be substantially noninductive it isnecessary that outer coil 62 be wound in a direct-ion opposite to thatof inner coil 50. Thus, the second length 60 of resistance wire is woundin a right-hand direction and is laid in the first row of notches 52 inthe outer mounting strips 34 nearest end plate 14. After the first rowof notches is occupied, the wire is laid in the second row and so onuntil all rows of notches have been utilized. It is to be understoodthat outer coil 62 is electrically connected in parallel with inner coil563 between the terminals 44 and 46.

While for purposes of illustration inner coil 59 has been described asbeing wound in the left-hand direction and outer coil 62 in theright-hand direction, it is to be understood that their directions ofwinding could be reversed.

After outer coil 62 is in place, insulating housing 26 is slid over theassembly and secured in place by means of the screws 24 and resistorunit It? is ready for installation.

Referring to FIGS. 3 and 4, the numeral 7t designates another embodimentof an inductive resistor unit incorporating the present invention whichdiifers from resistor unit It principally in that it is provided withonly one coil 72. Mounting strip '73 replaces the two mounting strips 32and 34, and has notches 74 similar to notches 52 in the outer mountingstrip 34. In all other respects, however, resistor unit 7b isconstructed of thesame components and in the same manner as resistorunit 10.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a resistor unit for immersion in an electrically nonconductiveliquid medium, in combination, a pair of spaced apart perforatedinsulating end plates, each end plate being provided with a plurality ofradially disposed slots, a plurality of insulating strips supportedbetween said end plates, each strip being disposed in registering slotsin said end plates, each strip having a plurality of notches in itsoutwardly facing edge, at least one coil of resistance wire wound onsaid strips so as to lie in the notches therealong, a pair of terminalsat opposite ends of said resistor unit, each terminal being mountedadjacent the outer surface of a respective end plate and electricallyconnected to one end of said coil, means for securing said plurality ofstrips in the slots of said end plates, and an insulating housingenclosing said strips and said coil.

2. In a resistor unit for immersion in an electrically nonconductiveliquid medium, in combination, a pair of spaced apart perforatedinsulating end plates, each end plate being provided with a plurality ofradially disposed slots, a plurality of insulating strips supportedbetween said end plates, each strip being disposed in registering slotsin said end plates and the ends of each strip projecting beyond theouter surface of the end plates, each strip having a plurality ofnotches in its outwardly facing edge, at least one coil of resistancewire wound on said strips so as to lie in the notches therealong, a pairof terminals, one terminal being mounted on the outwardly projecting endof one of said strips near one end plate and electrically connected toone end of said coil, the other terminal being mounted on the outwardlyprojecting end of one of said strips near the other end plate andelectrically connected to the other end of said coil, means for securingsaid plurality of strips to said end plates, said means comprising awire for engaging the outwardly projecting ends of said strips near oneend plate, and an insulating housing enclosing said strips and saidcoil.

3. In a resistor unit for immersion in an electrically nonconductiveliquid medium, in combination, a pair of spaced apart perforatedinsulating end plates, a plurality of inner insulating strips supportedbetween said end plates, an inner coil of resistance wire wound on saidinner strips, a plurality of outer insulating strips supported betweensaid end plates, an outer coil of resistance material wound on saidouter strips, a pair of terminals at opposite ends of said resistorunit, each terminal being mounted adjacent the outer surface of one ofsaid end plates and electrically connected to one end of said inner coiland one end of said outer coil, and an insulating housing enclosing saidinner and outer strips and said inner and outer coils.

4. The combination according to claim 3 wherein said inner and outercoils are wound in opposite directions so that the resistor unit issubstantially noninductive.

5. In a resistor unit for immersion in an electrically nonconductiveliquid medium, in combination, a pair of spaced apart perforatedinsulating end plates, each end plate having a plurality of radiallydisposed slots, a plurality of inner and outer insulating stripssupported between said end plates, each pair of registering slots insaid end plates accommodating an inner strip and an outer strip, eachinner strip and each outer strip having a plurality of notches in itsoutwardly facing edge, means for securing said inner and outer strips tosaid end plates, an inner coil of resistance wire wound on said innerstrips so as to lie in the notches thereof, an outer coil of resistanceWire wound on said outer strips so as to lie in the notches thereof, apair of terminals, one terminal being mounted on the outwardlyprojecting end of one of said strips near one end plate and electricallyconnected to one end of said inner coil and one end of said outer coil,the other terminal being mounted on the outwardly projecting end of oneof said strips near the other end plate and electrically connected tothe other end of said inner coil and the other end of said outer coil,and an insulating housing enclosing said inner and outer strips and saidinner and outer coil.

6. The combination according to claim 5 wherein said inner and outercoils are wound in opposite direction so that the resistor unit issubstantially noninductive.

References Cited in the file of this patent UNITED STATES PATENTS1,840,168 Mucher Jan. 5, 1932 3,017,255 Norris Ian. 16, 1962 FOREIGNPATENTS 566,559 Great Britain Ian. 3, 1945

1. IN A RESISTOR UNIT FOR IMMERSION IN AN ELECTRICALLY NONCONDUCTIVELIQUID MEDIUM, IN COMBINATION, A PAIR OF SPACED APART PERFORATEDINSULATING END PLATES, EACH END PLATE BEING PROVIDED WITH A PLURALITY OFRADIALLY DISPOSED SLOTS, A PLURALITY OF INSULATING STRIPS SUPPORTEDBETWEEN SAID END PLATES, EACH STRIP BEING DISPOSED IN REGISTERING SLOTSIN SAID END PLATES, EACH STRIP HAVING A PLURALITY OF NOTCHES IN ITSOUTWARDLY FACING EDGE, AT LEAST ONE COIL OF RESISTANCE WIRE WOUND ONSAID STRIPS SO AS TO LIE IN THE NOTCHES THEREALONG, A PAIR OF TERMINALSAT OPPOSITE ENDS OF SAID RESISTOR UNIT, EACH TERMINALS BEING MOUNTEDADJACENT THE OUTER SURFACE OF A RESPECTIVE END PLATE AND ELECTRICALLYCONNECTED TO ONE END OF SAID COIL, MEANS FOR SECURING SAID PLURALITY OFSTRIPS IN THE SLOTS OF SAID END PLATES, AND AN INSULATING HOUSINGENCLOSING SAID STRIPS AND SAID COIL.